1. Field of the Invention
This invention relates to a method for driving a liquid-jet head in which a portion of a pressure generating chamber communicating with a nozzle orifice for jetting a liquid is constituted of a vibration plate, a piezoelectric element is formed on the surface of the vibration plate, and the liquid is jetted by displacement of the piezoelectric element, and a liquid-jet apparatus equipped with the liquid-jet head.
2. Description of the Related Art
An example of a liquid-jet apparatus is an ink-jet recording apparatus comprising an ink-jet recording head equipped with a plurality of pressure generating chambers for generating pressure for ejection of ink droplets by piezoelectric elements or heating elements; a common reservoir for supplying ink to the respective pressure generating chambers; and nozzle orifices communicating with the respective pressure generating chambers. This ink-jet recording apparatus applies ejection energy to ink within the pressure generating chamber communicating with the nozzle orifice corresponding to a printing signal to eject ink droplets through the nozzle orifice.
The ink-jet recording head is constituted such that a portion of the pressure generating chamber communicating with the nozzle orifice for ejecting ink droplets is composed of a vibration plate, and the vibration plate is deformed by a piezoelectric element to pressurize ink within the pressure generating chamber, thereby ejecting ink droplets through the nozzle orifice. Two types of the ink-jet recording head have found practical use. One of them is a recording head using a piezoelectric actuator of a longitudinal vibration mode which expands and contracts in the axial direction of the piezoelectric element. The other is a recording head using a piezoelectric actuator of a flexural vibration mode.
The former recording head can change the volume of the pressure generating chamber by abutting the end surface of the piezoelectric element against the vibration plate, and enables manufacturing of a head suitable for high density printing. However, this recording head requires a difficult step of cutting and dividing the piezoelectric element in a comb tooth shape in conformity with the array pitch of the nozzle orifices, and also requires an operation for aligning and fixing the divisions of the piezoelectric element to the pressure generating chambers. Consequently, the manufacturing process is complicated.
In the latter recording head, on the other hand, the piezoelectric element can be fabricated and installed on a vibration plate by a relatively simple process which comprises adhering a green sheet of a piezoelectric material in conformity with the shape of the pressure generating chamber, and then sintering the green sheet. However, a certain size of the vibration plate is required because of the usage of flexural vibration, thus posing difficulty in achieving a high density array of the piezoelectric elements.
To resolve the disadvantage of the latter recording head, a recording head has been worked out, in which a uniform piezoelectric material layer is formed throughout the surface of the vibration plate by a film deposition technology, and the piezoelectric material layer is cut and divided into shapes corresponding to the pressure generating chambers by a lithography method, so that piezoelectric elements are formed independently of each other for the respective pressure generating chambers, thereby achieving a high density array of the piezoelectric elements.
As a driving signal for driving the piezoelectric element of the ink-jet recording head, a drive waveform comprising a square wave has been used. The drive waveform comprising the square wave includes a step of performing discharging from an intermediate driving voltage on standby to expand the pressure generating chamber, thereby sucking ink into the pressure generating chamber, a step of maintaining a minimum driving voltage, a step of performing charging to cause contraction of the pressure generating chamber, thereby ejecting ink, a step of maintaining a charging final voltage, and a step of performing discharging to return to the intermediate driving voltage. Ink droplets have been ejected by this drive waveform (see, for example, Japanese Unexamined Patent Publication No. 1998-250061 (pages 3–4, FIG. 3).
However, when the piezoelectric element of the multi-nozzled ink-jet recording head is driven with the use of the above-described conventional drive waveform comprising the square wave, an electric current (electric charges moving in the circuit) becomes high. This high current destroys the driving IC and driving wiring, thus posing the problem that a high density array of the piezoelectric elements and multiple-nozzle arrangement are difficult to attain.
This problem is not limited to the ink-jet recording head for ejection of ink. Needless to say, the problem exists similarly with other liquid-jet heads for ejection liquids other than ink.